Although fuel is often stored in underground tanks, such as tanks at gas stations, there are situations where it is preferred to store flammable liquids such as aviation fuel in above-ground tanks. Whether the fuel storage is below or above ground, there are environmental and safety considerations.
In below-ground tanks, dual-walled pipe systems have been developed whereby if a pipe leaks between the storage tank and the dispenser, the leakage is captured and not allowed to seep into the ground. In U.S. Pat. No. 4,895,272 this is taken care of by the provision of a containment dike below the storage tank to receive liquid if the tank leaks or overflows. Discharge of the volatile liquid onto the ground is prevented.
When the tank system is above ground, the fuel in the tank will expand and contract depending on the temperature of the air around the tank. A vent is provided at the top of the tank to allow for changes in the air space at the top of the tank between the surface of the liquid and a vent.
To accommodate fuel expansion, a tank should not be filled to the top. It should be filled to a prescribed point and then the filling should be stopped. However, when an operator fills the tank it is sometimes filled beyond the desired level. The fuel does not overflow; but the airspace at the top of the tank is less than desired or required. Then when the fuel expands on a hot day, for example, some of the fuel may escape through the vent, overflow, and pass from the tank down into the containment dike. The overflow does not drop onto the ground because it is prevented from doing so by the dike. However, the dike becomes contaminated with fuel, the fuel spreading out over the floor of the dike. There is the smell of gasoline until the liquid evaporates.
One object of this prevention is to provide a chamber around the vent at the top of a tank positioned in a containment dike, means being provided whereby when a small amount of fuel overflows the vent, it is retained at the vent and does not flow down into the dike.
Another object in the invention is to form a small chamber within the collar around the vent at the top of the tank having means positioned to block the flow of fuel escaping from the vent to a downwardly extending passage along the side of the tank into the dike.
Another object of this invention is to provide a simple low cost liquid control design around the vent at the top of a tank that utilizes the surface of the tank and the collar around the vent as part of the overflow liquid holding structure.
A further object of this invention is to provide a first overflow chamber at a vent at the top of a tank and a second larger overflow chamber in a containment dike, fuel overflowing said tank being able to reach the dike only after it exceeds the capacity of the first and second holding chambers.
Other objects of this invention will be apparent hereinafter from the specification and from the recital in the appended claims.